1. Field of the Invention
The present invention relates to a method for producing an amino acid. In particular, the present invention relates to an L-amino acid-producing bacterium belonging to the genus Escherichia and a method for producing L-amino acids using the bacterium, more specifically, L-glutamic acid, L-lysine, L-threonine, L-alanine, L-histidine, L-proline, L-arginine, L-valine, and L-isoleucine.
2. Brief Description of the Related Art
To improve production of L-amino acids by fermentation, strains isolated from nature or artificial mutants thereof have been used. For example, many artificial mutants which produce L-lysine are known, and most of them are resistant to S-2-aminoethylcysteine (AEC) and belong to the genus Brevibacterium, Corynebacterium, Bacillus, or Escherichia. Also, various techniques have been proposed to increase amino acid production, such as using a strain which has been transformed with recombinant DNA (U.S. Pat. No. 4,278,765).
The reported techniques are largely based on enhancing an activity of an enzyme involved in an amino acid biosynthetic pathway, conversion of the enzyme to one that is desensitized in inhibition, and the like (As to bacterium belonging the genus Escherichia, see Japanese Patent Application Laid-Open No. 56-18596 (1981) and International Publication No. WO 95/16042).
Alternatively, a bacterium belonging to the genus Corynebacterium in which the L-lysine excretion gene lysE is enhanced is known, and is an example of improving amino acid productivity by enhancing an amino acid excretion protein. However, as to bacteria belonging to the genus Escherichia, it is unknown whether an L-amino acid excretion protein exists or not. Therefore, it is unknown whether or not enhancing an L-amino acid excretion protein would be effective for L-amino acid production when using a bacterium belonging to the genus Escherichia. 
Although the entire nucleotide sequence of E. coli strain K-12 has been determined (Science, 277, 1453-1474 (1997)), there are a large number of proteins for which their functions remain unknown.